THIS IS DLC! The base game, Wyrmsun, is FREE on Steam. If you want to enter for this DLC and don't own the base game, you should be able to just add it over there, Sync your account, and then go ahead.

Once upon a time, a game key was a sacred thing: you bought it, you owned it. Not any more, alas. Keys get revoked these days for no reasons in the world.

This key is an old one. I keep track of these things as best I can, and my records say I haven't used it and I haven't given it away, so it should be as valid as the day I bought it. If it isn't, please let me know and I'll check to make sure there wasn't any mistake on my end. If I can fix the issue, I certainly will.